Patent GB-483072-A (GB)
Title: Improvements in methods of and apparatus for measuring ion-concentration
IPC: G01N27/30
Filed: 1936-07-06
Abstract: 483,072. Potentiometers ; determining physical qualities. KENT, Ltd., G. July 6, 1936, No. 18766. Void.. Convention date, Jan. 10. [Class 37] Apparatus for determining the ion-concentration of a solution comprises a hydrogen-ion electrode and a reference electrode which are situated in a flow-channel having an inlet so located that solution entering the flow-channel impinges directly on the active surface of the hydrogen-ion electrode so as to render turbulent the solution on and adjacent this active surface. In addition, a gas such as air may be introduced into the stream of solution prior to its entry into the flow-channel to increase the agitation of the solution at the electrode. The cell may comprise a glass electrode G and a reference electrode R held in housings F. The electrode G comprises a glass tube 3 with a thin-walled bulb 4, within which is situated a second tube 6 having a bulb 7 and an opening 8, the bulb 7 being partly filled with solid quinhydrone while the remainder of the tube 6 is filled with dilute hydrochloric acid, which is also arranged in the outer tube 3 to a level above the hole 8. A copper conductor 9 extends downwardly through the tube 6 and is connected to an electrode 9a of platinum, gold &c. Alternatively, an electrode of chloridized silver-plated platinum or chloridized silver may be used, in which case hydrochloric acid only is contained by the tube 6. The reference electrode comprises a tube 10 to which is attached by a ground glass joint a capsule 11. A tube 12 provided with a bulb 12a and a hole 14 is arranged within the tube 10 and the bulb 12a is partially filled with mercury to which is added mercurous chloride and potassium chloride crystals, the mixture being moistened with a saturated solution of potassium chloride and agitated to form an emulsion of mercurous chloride and mercury ; finally, the tube 10 is filled with potassium chloride solution to a level above a pipe 21 which acts as an overflow for the liquid to be tested. The liquid under test enters the cell through a pipe 17 and, due to the fact that the fluid impinges directly on the bulb 4, the electrode immediately acquires the potential corresponding to the ion-concentration of the liquid. This effect may be increased by introducing air into the stream of solution flowing into the pipe 17 by causing it to drip into a chamber connected to the other end of the pipe. An overflow pipe 22 is provided for the first chamber of the cell while the second chamber is connected to the first by a tube 20 which may also enter at the bottom of the chamber so that the reference electrode is continually washed by fresh liquid impinging thereon. Alternatively, this tube 20 is arranged approximately in the middle of the second chamber, the outlet pipe 21 being connected to the bottom of the chamber, or adjacent but somewhat above the inlet tube. In a modification, a test electrode of the antimony type is used and comprises a block of antimony embedded in a rubber support and arranged adjacent the inlet tube of the cell, while in a further form shown in Fig. 7, a quinhydrone type of electrode is used. Quinhydrone solution from a reservoir 32 is then fed through a valve-controlled pipe 33 to a pipe 18 along which the liquid under test is flowing to the ion-concentration cell. The test electrode 34 is a disc of platinum or gold arranged adjacent the inlet pipe 17, while the reference electrode R is of the type described above. The liquid under test is caused to issue from a pipe 18a as a jet so as to cause it to take up air which aids in agitating the liquid when it strikes the test electrode. Both electrodes may be arranged in a common vessel, the test electrode being situated in the path of the incoming liquid, or alternatively, where continuous measurement of a flowing stream of liquid is not required, the liquid may be contained in a bath which is agitated by a stirrer. The measurement is preferably effected by the system disclosed in British Specification 477,849. U.S.A. Specification 1,935,732 also is referred to.